Horizontal stringing over distance

agrodgers

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I've been trying to figure out/solve a problem I'm having where a particular type of bullet is changing impact horizontally from 200yds to 300yds by a significant amount. I'm shooting an A-Bolt II 6.5CR with a 22" barrel, 1-8" twist. I'm reloading 143gr ELD-X's and have tried a few powders (IMR4350, RL26, RL17, Superformance) but get the same basic results. My point of impact moves 6-8" horizontally when I move between 200yds & 300yds. Groups remain generally tight. Different powders give different results obviously, but I've been able to find a node that exhibited sub 1" at 200yds and about 1" at 300yds. I haven't tried altering seating depth yet but I'm very far off the lands as the magazine length limit won't allow me to get anywhere close ( I am at the limit there, so seating them deeper would be the only option). I've worked through ladder tests for each of the powders and checked the 200 & 300 ranges at the same time so there is no particular node that doesn't exhibit this tendency (i.e. I've shot 3 shot groups at 300yds for the ladder test then fire a 4th round at the 200 range - all of the 200yd shots move to the left the 6-8"). I've chrono'd all but the RL26 (I need a new chrono :-( ) and was achieving between 2700-2800fps for the other powders. I have a load worked up for 123gr SST's that shoots clover leafs at 200yds and ~0.5" groups at 300yds (when I do my part) without this phenomenon so I know the gun is capable. I've worked on some loads for the 130gr AB and ABLR without showing this phenomenon although I wasn't achieving groups as good as the SST's. While I'm probably ready to just give up on the ELD-X's for this gun, I still want to figure out the underlying physics of problem.
My initial thoughts on the problem are:
1). While 1-8" twist rate should be better for heavier bullets but combined with a drop in velocity (heaviest bullet I've tested) is this causing the bullet to not keep it's spin rate up causing it to "roll" to the right? That was one of the reasons I tried the RL26 as lots of people seem to be getting up into the 2950-3000fps range (with longer barrels). This speed would have been closer to the other loads that don't show this issue. Without the chrono I don't know how fast these loads were traveling however I went from 46.0gr - 49.0gr and there wasn't a significant difference in the horizontal stringing. If speed were the case, I would think it might get better/worse over a range and I don't think ~2" difference is enough. I've seen the same variation on other guns/ladder tests.
2). Seating depth - since I'm pretty far off the lands and the bullet may not be entering perfectly aligned I could understand a lot of variation. Could the particular curve of the ELD-X contribute to that? However, since I am getting good groups out of them at both the 200 & 300yds this seems unlikely. I would expect the groups to open up if there was inconsistency in how the bullet aligned itself.
3). maybe it's just the barrel and the heavier bullet. It is a sporter contour (not sure of the specific contour) but thin and light. The whole setup with scope (Leupold 4.5x14 VX3 CDS) is about 6.5lbs. I've read (probably on this site) that part of the movement of the barrel is not only vibration but an unwinding and stretching as well. I would assume that this unwinding/stretching would be effected much more in a light/thin barrel with a heavier bullet. Since I've varied the powder and done this over a ladder test, I would think I would see greater variation in the effect. I'll also try some other 140ish gr bullets going forward to see if they exhibit the same effect.

OK, anyone else have a thought on what is happening here?
 

Barrelnut

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If I read you right, she is shooting a sub 1" group at 200 yards and about a 1" at 300 yards. Issue is the whole 300 yard group is moving to the right 6~8 Inches....
Horizontal aside, that's a great shooting rifle.

I don't think that much consistent movement is caused by barrel harmonics, powder, or speed. There may be an issue with the scope or with the alignment of the scope to the barrel. Are you dialing elevation or using holdover for 300 yards? The scope needs to be pretty much aligned directly over the top of the barrel, if it is not and say aligned to the left, and the rifle is zeroed at 100 or 200, the impact will start to move to the right at 300 yards. Usually not as pronounced as this one though. Check to make sure you don't have something like the image below going on. There are some tools for checking and correcting this.
scope alignment.jpg
 

agrodgers

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Oh, welcome to the forum!
Thanks! one of those long time listener first time callers.....

As to the scope. I'll double check things there (no stone unturned) but I was pretty careful when I mounted it making sure it wasn't canted (used scope levels) and aligned with the barrel (less precise but edge of house through scope and barrel) ....but anything is possible. May just have to buy the laser boresighter ;-). The confusion for me there would be if the 123gr SST's shoot the way I expect them too, why wouldn't any other bullet. Also, I have not been adjusting the scope when moving from 300 to 200, i.e. no changes to the top turret (or side, obviously) & I'm picking the same point of aim on the target. Once I figured out that it was jumping that far (center line shots at 300, then move back to 200 yds and nothing on the paper....except I'd see some half moon holes on the very edge of the left side sometimes, then added some paper out there) I started aligning my 300 and 200 yd aim point for the center horizontal line and the vertical line passing through the right upper/lower smaller diamonds on the target. Then I'd hit essentially center on the vertical at 300 and between the large diamond in the center and the vertical center between the left smaller diamonds. So I'm picking the same aimpoint with no adjustments. Obviously I get different vertical impacts for the distances but the horizontal diff's have been driving me crazy!
I did have one issue with the scope while I was working up the load for the SST's and sent it back to Leupold, they checked it out and put new springs in the turrets. I shot 2 squares after that and it tracked really well so I'm thinking there isn't any issue there. But again, at least on these experiments I'm not moving those and I'm able to jump back and forth between 200-300 and they go right back to where I have grown to expect them.
 

Barrelnut

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Sorry, missed the part about the 123 SST shooting so well. Does seem to point to the bullet and the short mag length. I wouldn't fight it. Others have talked about ELD-X and seating depth sensitivity for various calibers on various threads.

I have been shooting some of the Berger 135 Classic Hunters. They have a good BC and I was not finding them depth sensitive. Might work......
 

agrodgers

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Thanks for the suggestions. Looking around this and other sites at the terminal characteristics for the Berger's, there seems to be a mixed bag. Some explosive fragmentation and some good channel exit wounds. I'm looking for experience with Elk specifically. It seems like antelope and deer will present no issues for penetration generally. My main worry (for any bullet) is the close in shots < 100yds where you have a less then optimal angle (quartering too, head on) and the bullets are really cooking. I've had a bad experience with the Nosler BT at ~50yds on an elk (300WM @ 3100fps) which forced me to switch to the AB. Most of my shots are typically in the 200-500yd range so a lot of these longer range bullets are probably going to perform well there....but for that 1 shot close in.... So any experience from people out there on elk sized targets for the Bergers would be appreciated as they sound like something I would want to explore. Of course another option for me is to just load up something pretty stout (Partitions?) that closely approximates the trajectory for the first 100yds and use those when I am wondering through the really thick stuff, then swap out to the longer range loads as needed.

Back to the main problem. Since I still have plenty of the ELD-X's laying around. I think I'm going to run an experiment on the seating depth/lands to see if I can prove that this is in fact the issue (not that it will cause me to use them now). I think I'll load up groups of 5 @ 0.015-0.02" off the lands and shoot at 100, 200, & 300yds (loading them singly) to see if I can get them to stop the stringing or at least alter the result somehow.
 

RT2506

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My suggestion is to use the Nosler Accubond you mentioned for the reason you mentioned. I did that with my 264 Win mag for the same reason, close in shots and high velocity. I use for deer hunting the 130 AB at 3350 fps from my 27 3/4" barrel. Bullet reacts the same weather it has been 25 or a touch over 500 yards. Goes in one shoulder takes out the vitals and exits with a quarter size hole the offside shoulder and deer is DRT. If I ever get to go elk hunting this will be what I will use. I have only recovered one of these bullets and it was from a buck shot at 111 yards almost length wise. Bullet entered front edge of left shoulder smashing it and was found against the smashed ball joint of the right hip. Bullet was a text book mushroom and weight was 87 grs. If it will do that on a deer it should work on an elk don't you think?
 

agrodgers

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So I finally had time to do a "little" reloading and then head to the range. I picked up some Partitions in 140gr (that's what they had in stock) for a ladder test. I found a pretty good node across ~1gr range...but the second part of the experiment was shooting between 200 & 300yds and seeing the affect. As the speed increased, the vertical alignment straightened out. At the low end of the ladder I was seeing the horizontal movement at a little under 4" but as I progressed I got to vertical alignment with some shots (due to user error :-( ) shooting a little left & right of the center line. Based on this I think that there is a combo of issues with this particular rifle. The speed needs to be sufficient for the heavier bullets & I need a little more forgiving round. The ELD-X's are too finicky for this barrel. One other thing I noticed was that during the ladder test my slower shots started out on the lower right side of the target and then progressed up and towards the left. I've never seen this before (all other tests I've ever run have been more vertical or slightly low left to upper right). Maybe I'm just trying to convince myself that there is an additional correlation but what to others see when they run their tests? In any case, I've got some 140 AB's ordered and I'll finish up working things out in time to take this out for Elk in Oct. Thanks for the feedback and suggestions!
 

tim_w

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Maybe you got a left hand twist lol

So since you were getting those horizontal mov from the elds you have shot the paritions and all the hor movment left but you are still getting wierd track of poi as vel changes? Have you actually tested the twist rate?

My first thought is of course cant or scope or mount iszue. But if they have been checked........
 
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agrodgers

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I have not. I've been assuming that the NIB gun/info that came with it was correct...which may be really bad on my part :(
 

DUSTY NOGGIN

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6-8 inches has to be scope somehow , does it have a pic rail and clamps?, are the front ring and back ring tightening screws both on the same side? is there a chunk of metal bound up inside the ring mounting rail area ? , is one of your ring clamps hitting/contacting the receiver anywhere -- i might would change the positions of the rings -- putting the one that is in the front in the rear and vise versa

have you tried anything past 300 ??
 
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agrodgers

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Dusty,
I've gone over the scope and made sure things aligned and are tight. Additionally, since the 123gr SST's don't exhibit the same tendency (and 130gr's that I've shot) wouldn't that eliminate the scope being canted? Depending on recoil (assuming more kick on the heavier bullets) I guess it wouldn't eliminate being loose, however, I get very good groupings for both the 200 and 300yd ranges. Very consistent, just the horizontal shift as I shoot from one to the other. If the scope was loose, I think I would get randomized movement within both the 200 & 300 yd groups. The 200yd groups were under 1" and the 300yd groups at about 1" and consistent results from range trip to range trip.

tim_w
I didn't have time last night (will make time tonight) to check the twist rate, and see what I get. Thanks for that suggestion.
 

Canhunter35

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Did you change body position that may affect poi?
Was the wind blowing very slightly? You can only feel a 4 mph wind on your face?
 

agrodgers

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Checked the twist rate, 8:1 as advertised.

Canhunter,
definitely changed body position from group to group (3shots @ 300yds & 1 shot @ 200yds) but as the POI consistency between each session is the same then that can be ruled out. Wind is almost always present but mostly from behind, we have small ribbon markers out on the range to see direction and speed. Additionally, I wouldn't expect as big of a shift in just 100 yds, at least between those to distances, without it being really gusty. 1" or so would be in the noise but 7-8" is way too much. I did think about maybe the barrel heating up as a factor as well (it does get pretty hot to the touch even after 4 shots) so I had reversed things as well (1 shot at 300yds first and 3 shots @ 200yds) but still get the same results and POI per yardage.

At some point I will run the seating depth experiment where I will be only able to load 1 round at a time (maybe next trip out) but since the Partitions look like they will work (AB's being shipped now as well) I figure I'll just finish out the workup on those and get some good practice in as the Antelope and Elk seasons will be here before I know it (86 days and counting).

Fortunately, one of my hunting buddies just bought a 6.5CR for his son to hunt with this year and it liked the ELD-X precision hunters right out of the box so we'll be able to use up all of the extra's I've got laying around now.

Thanks for all of the thoughts/questions/ideas from everybody!
 

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